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§Anatomy of a Play application

§The Play application layout

The layout of a Play application is standardized to keep things as simple as possible. After the first successful compilation, the project structure looks like this:

app                      → Application sources
 └ assets                → Compiled asset sources
    └ stylesheets        → Typically LESS CSS sources
    └ javascripts        → Typically CoffeeScript sources
 └ controllers           → Application controllers
 └ models                → Application business layer
 └ views                 → Templates
build.sbt                → Application build script
conf                     → Configurations files and other non-compiled resources (on classpath)
 └ application.conf      → Main configuration file
 └ routes                → Routes definition
dist                     → Arbitrary files to be included in your projects distribution
public                   → Public assets
 └ stylesheets           → CSS files
 └ javascripts           → Javascript files
 └ images                → Image files
project                  → sbt configuration files
 └ build.properties      → Marker for sbt project
 └ plugins.sbt           → sbt plugins including the declaration for Play itself
lib                      → Unmanaged libraries dependencies
logs                     → Logs folder
 └ application.log       → Default log file
target                   → Generated stuff
 └ resolution-cache      → Info about dependencies
 └ scala-2.13
    └ api                → Generated API docs
    └ classes            → Compiled class files
    └ routes             → Sources generated from routes
    └ twirl              → Sources generated from templates
 └ universal             → Application packaging
 └ web                   → Compiled web assets
test                     → source folder for unit or functional tests

§The app/ directory

The app directory contains all executable artifacts: Java and Scala source code, templates and compiled assets’ sources.

There are three packages in the app directory, one for each component of the MVC architectural pattern:

• app/controllers
• app/models
• app/views

You can add your own packages, for example, an app/utils package.

Note that in Play, the controllers, models, and views package names are simply conventions that can be changed if needed (such as prefixing everything with com.yourcompany).

There is also an optional directory called app/assets for compiled assets such as LESS sources and CoffeeScript sources.

§The public/ directory

Resources stored in the public directory are static assets that are served directly by the Web server.

This directory is split into three sub-directories for images, CSS stylesheets and JavaScript files. You should organize your static assets like this to keep all Play applications consistent.

In a newly-created application, the /public directory is mapped to the /assets URL path, but you can easily change that, or even use several directories for your static assets.

§The conf/ directory

The conf directory contains the application’s configuration files. There are two main configuration files:

• application.conf, the main configuration file for the application, which contains configuration parameters
• routes, the routes definition file.

If you need to add configuration options that are specific to your application, it’s a good idea to add more options to the application.conf file.

If a library needs a specific configuration file, it is good to provide it under the conf directory.

§The lib/ directory

The lib directory is optional and contains unmanaged library dependencies, ie. all JAR files you want to manually manage outside the build system. Just drop any JAR files here and they will be added to your application classpath.

§The build.sbt file

Your project’s main build declarations are generally found in build.sbt at the root of the project. The .scala files in the project/ directory can also be used to declare your project’s build.

§The project/ directory

The project directory contains the sbt build definitions:

• plugins.sbt defines sbt plugins used by this project.
• build.properties contains the sbt version to use to build your app.

§The target/ directory

The target directory contains everything generated by the build system. It can be useful to know what is generated here:

• classes/ contains all compiled classes (from both Java and Scala sources).
• classes_managed/ contains only the classes that are managed by the framework (such as the classes generated by the router or the template system). It can be useful to add this class folder as an external class folder in your IDE project.
• resource_managed/ contains generated resources, typically compiled assets such as LESS CSS and CoffeeScript compilation results.
• src_managed/ contains generated sources, such as the Scala sources generated by the template system.
• web/ contains assets processed by sbt-web such as those from the app/assets and public folders.

§Typical .gitignore file

Generated folders should be ignored by your version control system. Here is the typical .gitignore file for a Play application:

logs
project/project
project/target
target
tmp
dist
.cache

§Default sbt layout

You also have the option of using the default layout used by sbt and Maven. In order to use this layout, you must disable the layout plugin and set up explicit monitoring for twirl templates:

lazy val root: Project = (project in file("."))
  .enablePlugins(PlayScala)
  // Use sbt default layout
  .disablePlugins(PlayLayoutPlugin)

This will stop Play from overriding the default sbt layout, which looks like this:

build.sbt                  → Application build script
src                        → Application sources
 └ main                    → Compiled asset sources
    └ java                 → Java sources
       └ controllers       → Java controllers
       └ models            → Java business layer
    └ scala                → Scala sources
       └ controllers       → Scala controllers
       └ models            → Scala business layer
    └ resources            → Configurations files and other non-compiled resources (on classpath)
       └ application.conf  → Main configuration file
       └ routes            → Routes definition
    └ twirl
       └ views             → Templates
    └ assets               → Compiled asset sources
       └ css               → Typically LESS CSS sources
       └ js                → Typically CoffeeScript sources
    └ public               → Public assets
       └ css               → CSS files
       └ js                → Javascript files
       └ images            → Image files
 └ test                    → Unit or functional tests
    └ java                 → Java source folder for unit or functional tests
    └ scala                → Scala source folder for unit or functional tests
    └ resources            → Resource folder for unit or functional tests
 └ universal               → Arbitrary files to be included in your projects distribution
project                    → sbt configuration files
 └ build.properties        → Marker for sbt project
 └ plugins.sbt             → sbt plugins including the declaration for Play itself
lib                        → Unmanaged libraries dependencies
logs                       → Logs folder
 └ application.log         → Default log file
target                     → Generated stuff
 └ scala-2.13
    └ cache
    └ classes              → Compiled class files
    └ classes_managed      → Managed class files (templates, ...)
    └ resource_managed     → Managed resources (less, ...)
    └ src_managed          → Generated sources (templates, ...)

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